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    <script>
        /**
         * isNaN: 如果这个值不是数字[NaN]，返回true，是数字返回false
         * is Not a number
         * 
         * 
         * 
         */
        console.log(isNaN('10')); // 遇到字符串的时候，先将值 Number一下，在用isNaN判断
        console.log(isNaN(10));
        console.log(isNaN('10px'));
        console.log(isNaN(null));
        console.log(isNaN(NaN));//true
    </script>
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